There is disclosed in EP-A-0084093, a shock wave generator disposed in a bath filled with coupling medium, a patient reclining on a couch and being immersed in said bath so that the focus of the shock wave generator is directed on to a concretion in the patient, which concretion is to be disintegrated by means of the shock waves.
DE-A-2351247 discloses a shock wave generator located at one focal point of a focusing chamber in the form of part of an ellipsoid of revolution, said chamber being covered by an elastic membrane. By way of this membrane, the focusing chamber is applied to the patient's body, without the interposition of an air gap, in such a way that the concretion to be destroyed is positioned at the second focal point of the ellipsoid.
According to EP-A-0131654, alignment can be effected by axial displacement of the focusing chamber covered by a membrane, in a coupling cylinder which is applied to the patient's body and is likewise bounded by a membrane, a coupling medium being provided between the two membranes and within the focusing chamber itself.
DE-A-3220751 discloses the use of a shock wave generator comprising a flexible, coupling medium transmission part bounded by a film which is adaptable to the patient's body. Coupling is performed manually by the application of a coupling gel.
An object of the present invention is to provide improved apparatus for shock wave therapy in which the transmission of bacteria and pathogens is avoided, coupling of the shock waves to the patient's body being achieved simply, and with virtually loss-free transfer of acoustic radiation from said transmission part to the patient's body.
According to the invention the membrane is releasably attached at its marginal area to the therapy table, the membrane being thereby replaceable.
The membrane is thus a disposable article, a new membrane being provided for each patient.
The marginal area of the membrane may be pneumatically clamped to the therapy table. The membrane may be placed over a trough, surrounding the porthole in the therapy table, the trough being arranged to be connected to a vacuum source. Said trough may be formed on a ring in the form of an upwardly projecting pad surrounding and defining the porthole. The membrane may comprise a ready-made section of film, or a web of film comprising a series of such sections and which can be moved a section at a time across the porthole. The membrane preferably has a thickness of the order of 50 to 500 .mu.m.
For low-loss coupling of the therapeutic transducer to the patient's body any gas which may collect in the transmission part when the membrane is changed must be removed. The gas may be removed by means of a device which operates beneath the membrane and within the transmission part to extract gas therefrom. Recesses may be machined into the upper marginal area of the part of the therapy table surrounding the porthole, so that gas in said transmission part can be extracted by way of the recesses, or an annular pipe having perforations in its inwardly and upwardly facing surface may be provided for extracting the gas. When using such gas extraction means, the membrane must be distended so that gas extraction takes place at the highest point of the membrane, at which gas bubbles collect.
Another means for extracting the gas comprises a tube which is extensible from the center of the therapeutic transducer, and which has a perforated extractor head at its tip. By extension of that tube the membrane undergoes a pyramid-shaped distortion, so that any gas bubbles which may be present in said transmission part make their way to the perforated extractor head located at the highest point that is to say at the apex of the pyramid. Such an effect can also be attained by the provision of a cranked extractor tube opening radially into said transmission part, and having a perforated extractor head at its free end, the extractor tube being rotatable about a radially guided part thereof. The extraction means described above are not, however, needed if the membrane is made of a material which is microporous and gas-permeable, but is impervious to water, being of polyurethane for example.